This project is concerned with virus-cell interactions and has resulted in the characterization of receptors for Paramyxoviruses and measles virus in erythrocytes and cultured mammalian cells. The program has expanded to include isolation and characterization of viral glycoproteins expressed on the surface of infected cells. Immune electron microscopy and immuno-freeze etching techniques have been applied to studies of fusion of erythrocytes by Paramyxoviruses (Sendai and measles viruses). In the course of these studies extensive analysis of human and simian erythrocytes have been completed. Current interest centers on measles virus and the peptide mapping of individual measles viral glycoproteins. Mutant cell lines selected on the basis of resistance to specific lectins are being studied for susceptibility/resistance to infection and/or fusion by several paramyxoviruses. These studies may further elucidate the specific nature of receptors for the individual viral groups. Receptors for nonenveloped hemagglutinating viruses (Reovirus type 3 and Adenovirus type 7) will be further characterized. We have determined that the cold hemagglutinin (IgM) which is evoked by human infection with Mycoplasma pneumoniae is cross-reactive with certain glycoproteins in human erythrocytes. These studies are based on immunochemical determinations as well as immune electron microscopy with erythrocytes, Mycoplasma pneumoniae and corresponding monospecific antisera.